One-dimensional scintillator film with benign grain boundaries for high-resolution and fast x-ray imaging

Fast and high-resolution x-ray imaging demands scintillator films with negligible afterglow, high scintillation yield, and minimized cross-talk. However, grain boundaries (GBs) are abundant in polycrystalline scintillator film, and, for current inorganic scintillators, detrimental dangling bonds at GBs inevitably extend radioluminescence lifetime and increase nonradiative recombination loss, deteriorating afterglow and scintillation yield. Here, we demonstrate that scintillators with one-dimensional (1D) crystal structure, Cs₅Cu₃Cl₆I₂ explored here, possess benign GBs without dangling bonds, yielding nearly identical afterglow and scintillation yield for single crystals and polycrystalline films. Because of its 1D crystal structure, Cs₅Cu₃Cl₆I₂ films with desired columnar morphology are easily obtained via close space sublimation, exhibit negligible afterglow (0.1% at 10 ms) and high scintillation yield (1.2 times of CsI:Tl). We have also demonstrated fast x-ray imaging with 27 line pairs mm^-1 resolution and frame rate up to 33 fps, surpassing most existing scintillators. We believe that the 1D scintillators can greatly boost x-ray imaging performance.

Charge Transfer and Charge Trapping Processes in Ca- or Al-Co-doped Lu2SiO5 and Lu2Si2O7 Scintillators Activated by Pr3+ or Ce3+ Ions

Lutetium oxyorthosilicate Lu₂SiO₅ (LSO) and pyrosilicate Lu₂Si₂O₇ (LPS) activated by Ce³⁺ or Pr³⁺ are known to be effective and fast scintillation materials for the detection of X-rays and γ-rays. Their performances can be further improved by co-doping with aliovalent ions. Herein, we investigate the Ce³⁺(Pr³⁺) → Ce⁴⁺(Pr⁴⁺) conversion and the formation of lattice defects stimulated by co-doping with Ca²⁺ and Al³⁺ in LSO and LPS powders prepared by the solid-state reaction process. The materials were studied by electron paramagnetic resonance (EPR), radioluminescence spectroscopy, and thermally stimulated luminescence (TSL), and scintillation decays were measured. EPR measurements of both LSO:Ce and LPS:Ce showed effective Ce³⁺ → Ce⁴⁺ conversions stimulated by Ca²⁺ co-doping, while the effect of Al³⁺ co-doping was less effective. In Pr-doped LSO and LPS, a similar Pr³⁺ → Pr⁴⁺ conversion was not detected by EPR, suggesting that the charge compensation of Al³⁺ and Ca²⁺ ions is realized via other impurities and/or lattice defects. X-ray irradiation of LPS creates hole centers attributed to a hole trapped in an oxygen ion in the neighborhood of Al³⁺ and Ca²⁺. These hole centers contribute to an intense TSL glow peak at 450-470 K. In contrast to LPS, only weak TSL peaks are detected in LSO and no hole centers are visible via EPR. The scintillation decay curves of both LSO and LPS show a bi-exponential decay with fast and slow component decay times of 10-13 ns and 30-36 ns, respectively. The decay time of the fast component shows a small (6-8%) decrease due to co-doping.

Energy Partitioning in Multicomponent Nanoscintillators for Enhanced Localized Radiotherapy

Multicomponent nanomaterials consisting of dense scintillating particles functionalized by or embedding optically active conjugated photosensitizers (PSs) for cytotoxic reactive oxygen species (ROS) have been proposed in the last decade as coadjuvant agents for radiotherapy of cancer. They have been designed to make scintillation-activated sensitizers for ROS production in an aqueous environment under exposure to ionizing radiations. However, a detailed understanding of the global energy partitioning process occurring during the scintillation is still missing, in particular regarding the role of the non-radiative energy transfer between the nanoscintillator and the conjugated moieties which is usually considered crucial for the activation of PSs and therefore pivotal to enhance the therapeutic effect. We investigate this mechanism in a series of PS-functionalized scintillating nanotubes where the non-radiative energy transfer yield has been tuned by control of the intermolecular distance between the nanotube and the conjugated system. The obtained results indicate that non-radiative energy transfer has a negligible effect on the ROS sensitization efficiency, thus opening the way to the development of different architectures for breakthrough radiotherapy coadjutants to be tested in clinics.

Nd:YAG Single Crystals Grown by the Floating Zone Method in a Laser Furnace

We report on single crystal growth of laser material Nd:YAG widely used in the applications by the innovative crucible-free floating zone method implemented in an advanced laser optical furnace. We have optimized the parameters for the production of high-quality single crystals of the size typical for laser rods. To reduce the strain and improve machinability, we have developed an afterheater to thermalize the grown part of a single crystal below the hot zone, which is a technique unavailable in common mirror furnaces. The high quality of the single crystals was verified by Laue diffraction, and the internal strain was documented by neutron diffraction. The absorption spectrum corresponds with the parameters of the commercially used material produced by the Czochralski method. The presented methodology for the single crystal growth by the floating zone method with laser heating is applicable for the preparation of other high-quality single crystals of oxide-based materials, particularly in an oxidizing environment unattainable in commonly used crucible methods.

Scintillation Characteristics of the Single-Crystalline Film and Composite Film-Crystal Scintillators Based on the Ce3+-Doped (Lu,Gd)3(Ga,Al)5O12 Mixed Garnets under Alpha and Beta Particles, and Gamma Ray Excitations

The crystals of (Lu,Gd)₃(Ga,Al)₅O₁₂ multicomponent garnets with high density ρ and effective atomic number Z_eff are characterized by high scintillation efficiency and a light yield value up to 50,000 ph/MeV. During recent years, single-crystalline films and composite film/crystal scintillators were developed on the basis of these multicomponent garnets. These film/crystal composites are potentially applicable for particle identification by pulse shape discrimination due to the fact that α-particles excite only the film response, γ-radiation excites only the substrate response, and β-particles excite both to some extent. Here, we present new results regarding scintillating properties of selected (Lu,Gd)₃(Ga,Al)₅O₁₂:Ce single-crystalline films under excitation by alpha and beta particles and gamma ray photons. We conclude that some of studied compositions are indeed suitable for testing in the proposed application, most notably Lu_1.5Gd_1.5Al₃Ga₂O₁₂:Ce film on the GAGG:Ce substrate, exhibiting an α-particle-excited light yield of 1790-2720 ph/MeV and significantly different decay curves excited by α- and γ-radiation.

Achieving Efficient Neutron and Gamma Discrimination in a Highly Stable 6Li-Loaded Cs3Cu2I5 Perovskite Scintillator

Low-dimensional Cu(I) perovskite halides with efficient exciton emissions have recently emerged as promising scintillation materials for X-ray and gamma-ray detection applications. Here, we demonstrate the possibility of using zero-dimensional Cs₃Cu₂I₅ for the sensitive detection of thermal neutrons and neutron-gamma discrimination enabled by Li doping. Single crystals of Cs₃Cu₂I₅ doped with 95% enriched ⁶Li were grown by the Bridgman method. Cs₃Cu₂I₅:⁶Li offers a compelling combination of high stability against moisture and oxygen, a decent energy resolution of 4.8% for 662 keV ¹³⁷Cs gamma-rays, a high light yield of 30 000 photons/MeV for gamma-rays, and 96 000 photons/neutron for thermal neutron, and a good neutron-gamma pulse shape discrimination figure of merit of 2.27. Our discovery of ⁶Li-doped low-dimensional perovskite halides opens up a new horizon for stable and high-performance neutron-gamma scintillator design.

Lead-Free Zero-Dimensional Organic-Copper(I) Halides as Stable and Sensitive X-ray Scintillators

Low-dimensional organic-metal halides are regarded as an emerging class of X-ray scintillation materials, but most of the discovered compounds are confronted with challenges of toxicity and instability. To address these challenges, we herein report two lead-free zero-dimensional (0D) hybrid halides, (Bmpip)₂Cu₂Br₄ and PPh₄CuBr₂ single crystals, grown by the low-cost solution-processing method. By single-crystal X-ray diffraction refinement, the crystal structures of (Bmpip)₂Cu₂Br₄ and PPh₄CuBr₂ were determined to be orthorhombic and monoclinic crystal systems, respectively. (Bmpip)₂Cu₂Br₄ and PPh₄CuBr₂ show broadband orange and yellow emissions peaking at 620 and 538 nm, respectively. Different from the emission nature of the recent reported Cu-based halide hybrids, both (Bmpip)₂Cu₂Br₄ and PPh₄CuBr₂ emit from excitons bound to defects featuring spin-allowed transition, enabling them to possess fast scintillation decay time of tens of nanoseconds, respectively. In particular, the (Bmpip)₂Cu₂Br₄ single crystal has a high photoluminescence quantum yield of 48.2%, a high scintillation yield of 16,000 photons/MeV, and a low detection limit of 710 nGy_air/s. Due to the combination of nontoxicity, long-term stability, and decent detection performance, (Bmpip)₂Cu₂Br₄ could be regarded as a promising X-ray scintillator.

The Sensitization of Scintillation in Polymeric Composites Based on Fluorescent Nanocomplexes

The sensitization of scintillation was investigated in crosslinked polymeric composite materials loaded with luminescent gold clusters aggregates acting as sensitizers, and with organic dye rhodamine 6G as the emitting species. The evolution in time of the excited states population in the systems is described by a set of coupled rate equations, in which steady state solution allowed obtainment of an expression of the sensitization efficacy as a function of the characteristic parameters of the employed luminescent systems. The results obtained indicate that the realization of sensitizer/emitter scintillating complexes is the strategy that must be pursued to maximize the sensitization effect in composite materials.

On the Role of Cs4PbBr6 Phase in the Luminescence Performance of Bright CsPbBr3 Nanocrystals

CsPbBr3 nanocrystals have been identified as a highly promising material for various optoelectronic applications. However, they tend to coexist with Cs4PbBr6 phase when the reaction conditions are not controlled carefully. It is therefore imperative to understand how the presence of this phase affects the luminescence performance of CsPbBr3 nanocrystals. We synthesized a mixed CsPbBr3-Cs4PbBr6 sample, and compared its photo- and radioluminescence properties, including timing characteristics, to the performance of pure CsPbBr3 nanocrystals. The possibility of energy transfer between the two phases was also explored. We demonstrated that the presence of Cs4PbBr6 causes significant drop in radioluminescence intensity of CsPbBr3 nanocrystals, which can limit possible future applications of Cs4PbBr6-CsPbBr3 mixtures or composites as scintillation detectors.

Non-Hygroscopic, Self-Absorption Free, and Efficient 1D CsCu2I3 Perovskite Single Crystal for Radiation Detection

A novel all-inorganic CsCu₂I₃ single-crystalline perovskite as a nonhygroscopic and efficient X-ray and γ-ray scintillator is described herein. It is featured by a one-dimensional (1D) perovskite structure with an orthorhombic system and a space group of Cmcm. The CsCu₂I₃ crystal emits yellow light peaking at 570 nm originated from strongly localized 1D exciton emission. It appears self-absorption free because of the large Stokes shift of 1.54 eV. The photophysics process of the self-trapped exciton was studied using temperature dependent photoluminescene spectra and decay kinetics measurements. The CsCu₂I₃ crystal exhibits an extremely low afterglow level of 0.008% at 10 ms under X-ray excitation. Under ¹³⁷Cs γ-ray irradiation, its light yield is 16 000 photons/MeV with an energy resolution of 7.8% at 662 keV.

Liquid phase epitaxy growth of high-performance composite scintillators based on single crystalline films and crystals of LuAG

Top – Scheme of the composite scintillator for registration of α-particles and γ-quanta. Bottom – Samples of the LuAG:Ce SCF/LuAG:Sc SC (a) and LuAG:Pr SCF/LuAG:Sc SC (b) composite scintillators prepared using the liquid phase epitaxy growth method.

Doping nanoparticles using pulsed laser ablation in a liquid containing the doping agent

While doping of semiconductors or oxides is crucial for numerous technological applications, its control remains difficult especially when the material is reduced down to the nanometric scale. In this paper, we show that pulsed laser ablation of an undoped solid target in an aqueous solution containing activator ions offers a new way to synthesise doped-nanoparticles. The doping efficiency is evaluated for laser ablation of an undoped Gd₂O₃ target in aqueous solutions of EuCl₃ with molar concentration from 10^-5 mol L^-1 to 10^-3 mol L^-1. Thanks to luminescence experiments, we show that the europium ions penetrate the core of the synthesised monoclinic Gd₂O₃ nanoparticles. We also show that the concentration of the activators in the nanoparticles is proportional to the initial concentration in europium ions in the aqueous solution, and a doping of about 1% ([Eu]/[Gd] atomic ratio) is reached. On the one hand, this work could open new ways for the synthesis of doped nanomaterials. On the other hand, it also raises the question of undesired penetration of impurities in laser-generated nanoparticles in liquids.

Core-shell ZnO:Ga-SiO2 nanocrystals: limiting particle agglomeration and increasing luminescence via surface defect passivation

Heat treatment is needed to increase the luminescence intensity of ZnO:Ga particles, but it comes at the cost of higher particle agglomeration. Higher agglomeration results in low transparency of scintillating powder when embedded in a matrix and constitutes one of the biggest disadvantages, besides low light yield and low stopping power, of ZnO:Ga powder. Limiting ZnO:Ga particle size is therefore a key step in order to prepare highly luminescent and transparent composites with prospects for optical applications. In this work, SiO2 coating was successfully used to improve luminescence intensity or limitation of crystallite size growth during further annealing. Furthermore, ZnO:Ga and ZnO:Ga-SiO2 core-shells were embedded in a polystyrene matrix.

Advancement toward ultra-thick and bright InGaN/GaN structures with a high number of QWs

InGaN/GaN structures are studied as potential candidates for superfast scintillation detectors and show the leading decay time of around 1 ns and intense luminescence.

Progress in fabrication of long transparent YAG:Ce and YAG:Ce,Mg single crystalline fibers for HEP applications

A significant enhancement in the light attenuation length in 22–55 cm long YAG:Ce and YAG:Ce,Mg fibers grown by the micro-pulling-down method has been reported.

Heavily Ce3+-doped Y3Al5O12 thin films deposited by a polymer sol–gel method for fast scintillation detectors

The performance of cerium-doped Y₃Al₅O₁₂ (Ce³⁺:YAG) often depends on cerium solubility achievable in a particular preparation technology.

LPE growth and study of the Ce3+ incorporation in LuAlO3:Ce single crystalline film scintillators

Scheme of the absorption and emission levels of Ce³⁺ and Pb²⁺ ions in the energy band scheme of the LuAP host (a) and fragment of the LuAP structure with Ce_Lu, Ce_Lu–Ce_Lu, Pb²⁺ and Pt³⁺ centers (b).

Ultrafast Zn(Cd,Mg)O:Ga nanoscintillators with luminescence tunable by band gap modulation

Photo-induced synthesis was used for preparation of powder Zn(Cd,Mg)O:Ga scintillating nanocrystals featuring properties of solid solutions. Only ZnO phase was identified without any phase separation up to 10% of Cd after optimization of the preparation. Radioluminescence spectra show the exciton-related emission in UV spectral range with significant blue (ZnMgO:Ga) or red (ZnCdO:Ga) shifts. The emission wavelength is tunable by the Cd/Mg content. Defect-related emission is completely suppressed after treatment in reducing atmosphere. Photoluminescence and cathodoluminescence decays show extremely fast component. Subnanosecond decay together with band gap modulation make Zn(Cd,Mg)O:Ga good candidate for practical applications like X-ray induced photodynamic therapy (PDTX) or those requiring superfast timing.

Line-tunable Er:GGAG laser

In this Letter, for the first time, to the best of our knowledge, a pulse and CW laser based on an Er-doped Gd₃Ga_2.7Al_2.3O₁₂ (Er:GGAG) active medium emitting laser radiation at 2.8 μm are presented. With the longitudinal diode pumping, the maximal output energy of 4.9 mJ and slope efficiency of 13.5% in the pulse regime were reached. Using the birefringent MgF₂ plate, the line tunability of Er:GGAG at several spectral bands of 2800-2822 nm, 2829-2891 nm, and 2917-2942 nm were obtained.

Octahedral molybdenum clusters as radiosensitizers for X-ray induced photodynamic therapy

The use of radiosensitizers recently emerged as a promising approach to circumvent the depth penetration limitations of photodynamic therapy of cancer and to enhance radiotherapeutical effects. A widely explored current strategy is based on complex nanoarchitectures that facilitate the transfer of energy harvested from X-ray radiation by scintillating nanoparticles to the surrounding photosensitizer molecules to generate reactive oxygen species, mostly singlet oxygen O₂(¹Δ_g). We describe an alternative approach aiming at a considerable simplification of the architecture. The presented nanoparticles, made of the luminescent octahedral molybdenum cluster compound (n-Bu₄N)₂[Mo₆I₈(OCOCF₃)₆], efficiently absorb X-rays due to the high content of heavy elements, leading to the formation of the excited triplet states that interact with molecular oxygen to produce O₂(¹Δ_g). The activity of the nanoparticles on HeLa cells was first investigated under UVA/blue-light irradiation in order to prove the biological effects of photosensitized O₂(¹Δ_g); there is no dark toxicity at micromolar concentrations, but strong phototoxicity in the nanomolar range. The nanoparticles significantly enhance the antiproliferative effect of X-ray radiation in vitro at lower concentration than for previously reported O₂(¹Δ_g) radiosensitizing systems and this effect is more pronounced on cancer HeLa cells than non-cancer MRC cells. The results demonstrate that the cluster-based radiosensitizers of O₂(¹Δ_g) have strong potential with respect to the enhancement of the efficacy of radiotherapy with exciting opportunities for cancer treatment.

Demonstration of cellular imaging by using luminescent and anti-cytotoxic europium-doped hafnia nanocrystals

Luminescent nanoparticles are researched for their potential impact in medical science, but no materials approved for parenteral use have been available so far. To overcome this issue, we demonstrate that Eu3+-doped hafnium dioxide nanocrystals can be used as non-toxic, highly stable probes for cellular optical imaging and as radiosensitive materials for clinical treatment. Furthermore, viability and biocompatibility tests on artificially stressed cell cultures reveal their ability to buffer reactive oxygen species, proposing an anti-cytotoxic feature interesting for biomedical applications.

LuAG:Pr3+-porphyrin based nanohybrid system for singlet oxygen production: Toward the next generation of PDTX drugs

A highly prospective drug for the X-ray induced photodynamic therapy (PDTX), LuAG:Pr³⁺@SiO₂-PpIX nanocomposite, was successfully prepared by a three step process: photo-induced precipitation of the Lu₃Al₅O₁₂:Pr³⁺ (LuAG:Pr³⁺) core, sol-gel technique for amorphous silica coating, and a biofunctionalization by attaching the protoporphyrin IX (PpIX) molecules. The synthesis procedure provides three-layer nanocomposite with uniform shells covering an intensely luminescent core. Room temperature radioluminescence (RT RL) spectra as well as photoluminescence (RT PL) steady-state and time resolved spectra of the material confirm the non-radiative energy transfer from the core Pr³⁺ ions to the PpIX outer layer. First, excitation of Pr³⁺ ions results in the red luminescence of PpIX. Second, the decay measurements exhibit clear evidence of mentioned non-radiative energy transfer (ET). The singlet oxygen generation in the system was demonstrated by the 3'-(p-aminophenyl) fluorescein (APF) chemical probe sensitive to the singlet oxygen presence. The RT PL spectra of an X-ray irradiated material with the APF probe manifest the formation of singlet oxygen due to which enhanced luminescence around 530 nm is observed. Quenching studies, using NaN₃ as an ¹O₂ inhibitor, also confirm the presence of ¹O₂ in the system and rule out the parasitic reaction with OH radicals. To summarize, presented features of LuAG:Pr³⁺@SiO₂-PpIX nanocomposite indicate its considerable potential for PDTX application.

Epitaxial growth of composite scintillators based on Tb3Al5O12 : Ce single crystalline films and Gd3Al2.5Ga2.5O12 : Ce crystal substrates

The composite scintillators based on the single crystalline films of TbAG : Ce garnet and GAGG : Ce crystal substrates was developed using the LPE growth method for simultaneous registration of α-particles and γ-quanta in mixed ionizing fluxes.

Spectroscopic and laser characterization of Yb0.15:(LuxY1-x)3Al5O12 ceramics with different Lu/Y balance

We report a broad comparative analysis of the spectroscopic and laser properties of solid solution Lutetium-Yttrium Aluminum Garnet (LuYAG, (Lu_xY_1-x)₃Al₅O₁₂) ceramics doped with Yb. The investigation was mainly aimed to assess the impact of the Lu/Y ratio on the Yb optical and laser properties. Therefore we analyzed a set of samples with different Y/Lu balance, namely 25/75, 50/50 and 75/25, with 15% Yb doping. We found that the Yb absorption and emission spectra changed from YAG to LuAG when gradually increasing in Lu content. Regarding the laser emission, remarkable results were achieved with all samples. Maximum output power was 8.2 W, 7.3 W and 8.7 W for Y/Lu balance 25/75, 50/50 and 75/25 respectively, at 1030 nm; the slope efficiency and the optical-to-optical efficiencies approached or exceeded 60% and 50% respectively. The tuning range was investigated using an intracavity ZnSe prism. The broadest tuning range (998 nm to 1063 nm) was obtained with Y/Lu balance 75/25, whereas the emission of the other two samples extended from 1000 nm to 1058 nm. To the best of our knowledge, this is the first comparative analysis of Yb:LuYAG ceramics or crystals as laser host across such a broad range of Y/Lu ratios.

Preparation and luminescence properties of ZnO:Ga - polystyrene composite scintillator

Highly luminescent ZnO:Ga-polystyrene composite (ZnO:Ga-PS) with ultrafast subnanosecond decay was prepared by homogeneous embedding the ZnO:Ga scintillating powder into the scintillating organic matrix. The powder was prepared by photo-induced precipitation with subsequent calcination in air and Ar/H₂ atmospheres. The composite was subsequently prepared by mixing the ZnO:Ga powder into the polystyrene (10 wt% fraction of ZnO:Ga) and press compacted to the 1 mm thick pellet. Luminescent spectral and kinetic characteristics of ZnO:Ga were preserved. Radioluminescence spectra corresponded purely to the ZnO:Ga scintillating phase and emission of polystyrene at 300-350 nm was absent. These features suggest the presence of non-radiative energy transfer from polystyrene host towards the ZnO:Ga scintillating phase which is confirmed by the measurement of X-ray excited scintillation decay with picosecond time resolution. It shows an ultrafast rise time below the time resolution of the experiment (18 ps) and a single-exponential decay with the decay time around 500 ps.

First laser emission of Yb0.15:(Lu0.5Y0.5)3Al5O12 ceramics

We report the first laser oscillation on Yb_0.15:(Lu_0.5Y_0.5)₃Al₁₂ ceramics at room temperature. At 1030 nm we measured a maximum output power of 7.3 W with a corresponding slope efficiency of 55.4% by using an output coupler with a transmission of T = 39.2%. The spectroscopic properties are compared with those of the two parent garnets Yb:YAG and Yb:LuAG. To the best of our knowledge these are the first measurements reported in literature achieved with this new host.

Optical, Structural and Paramagnetic Properties of Eu-Doped Ternary Sulfides ALnS₂ (A = Na, K, Rb; Ln = La, Gd, Lu, Y)

Eu-doped ternary sulfides of general formula ALnS₂ (A = Na, K, Rb; Ln = La, Gd, Lu, Y) are presented as a novel interesting material family which may find usage as X-ray phosphors or solid state white light emitting diode (LED) lighting. Samples were synthesized in the form of transparent crystalline hexagonal platelets by chemical reaction under the flow of hydrogen sulfide. Their physical properties were investigated by means of X-ray diffraction, time-resolved photoluminescence spectroscopy, electron paramagnetic resonance, and X-ray excited fluorescence. Corresponding characteristics, including absorption, radioluminescence, photoluminescence excitation and emission spectra, and decay kinetics curves, were measured and evaluated in a broad temperature range (8-800 K). Calculations including quantum local crystal field potential and spin-Hamiltonian for a paramagnetic particle in D3d local symmetry and phenomenological model dealing with excited state dynamics were performed to explain the experimentally observed features. Based on the results, an energy diagram of lanthanide energy levels in KLuS₂ is proposed. Color model xy-coordinates are used to compare effects of dopants on the resulting spectrum. The application potential of the mentioned compounds in the field of white LED solid state lighting or X-ray phosphors is thoroughly discussed.

Characterization of the lasing properties of a 5%Yb doped Lu₂SiO₅ crystal along its three principal dielectric axes

The laser performance of a 5% Yb doped Lu2SiO5 (Yb:LSO) has been investigated in quasi continuous-wave pumping regime along the three principal dielectric axes of the crystal, to obtain a complete characterization of its laser properties. The comparison among the obtained results for differently polarized lasers, in term of relative slope efficiency and absolute efficiency, allows the exploitability of different orientations of the material in order to be determined to obtain efficient laser sources. The laser slope efficiency and the energy conversion efficiency were similar for emission polarized along the three indicatrix axes, with noticeable maximum values of slope efficiency around 90% for polarization along the Y and Z axes. Tunable laser action has been obtained in the range 990 nm - 1084 nm, with sizeable differences in the shape of the tuning curve for polarization along the X, Y and Z axes. In particular, the tuning for polarization along the Z axis is relatively flat and uniform in the range 1023 nm - 1083 nm.

InGaN/GaN multiple quantum well for fast scintillation application: radioluminescence and photoluminescence study

We prepare InGaN/GaN multiple quantum well (MQW) structure by metal-organic vapour phase epitaxy and characterize it by fine XRD measurements. We demonstrate its suitability for scintillator application including a unique measurement of wavelength-resolved scintillation response under nanosecond pulse soft x-ray source in extended dynamical and time scales. The photoluminescence and radioluminescence were measured: we have shown that the ratio of the intensity of quantum well (QW) exciton luminescence to the intensity of the yellow luminescence (YL) band IQW/IYL depends strongly on the type and intensity of excitation. Slower scintillation decay measured at YL band maximum confirmed the presence of several radiative recombination centres responsible for wide YL band, which also partially overlap with the QW peak. Further improvements of the structure are suggested, but even the presently reported decay characteristics of the excitonic emission in MQW are better compared to the currently widely used single crystal YAP:Ce or YAG:Ce scintillators. Thus, such a type of a semiconductor scintillator is highly promising for fast detection of soft x-ray and related beam diagnostics.